Oxygen-starved oceans rapidly dying

The world’s coastal oceans are in crisis, with oxygen-starved ”dead zones” increasing by a third in just two years as global temperatures increase with climate change, according to the International Whaling Commission’s latest scientific report.

Dead zones, caused by over-enrichment of waters by nutrients from run-off, sewerage and warming waters, represent ”the worst-case scenario for coastal biodiversity” and are the ‘’severest form” of ocean habitat degradation, the report says.
The number of ocean dead zones has grown from 44 areas reported in 1995 to more than 400, with some of the worst oxygen-starved areas extending over 22,000sqkm.

Recent figures from the United Nations Environment Program estimate fertilisers, sewage and other other pollutants, combined with the impact of climate change, have led to a doubling in the number of oxygen-deficient dead zones every decade since the 1960s.

The growing list of dead zones includes waters in the Gulf of Mexico, South China Sea, Gulf of Finland, Adriatic Sea and areas of the Caribbean. The Black Sea between south-eastern Europe and Turkey which has one of the largest dead zones in the world, had 26 commercial fish species in the 1960s but now has only five.

A recent study listed New Zealand’s oldest marine reserve, Cape Rodney, as one of the world’s 10 worst-affected areas, and also listed coastal areas near Perth and around Tasmania both areas on whale migration routes as areas of emerging concern.

The commission’s 2008 State of the Cetacean Environment Report lists a growing number of concerns over the impacts of climate change and ocean pollution on the world’s whales, dolphins and porpoises.

The report says low-oxygen waters at depths of 300m to 700m have expanded in tropical oceans over the past 50 years as the oceans warm. Areas previously rich in oxygen have become ”oxygen minimum zones” containing less than 120 micromoles of oxygen per kilogram of water. It says these reduced oxygen areas will have ”dramatic consequences” for marine ecosystems because fish, squid and crustaceans cannot survive in them. The worst-affected areas are in tropical regions of the Atlantic Ocean, west of Africa and the equatorial areas of the Pacific .

Canberra Times